Traffic signal controller

ABSTRACT

Structural arrangements are disclosed for achieving stepped advancement of a cam drum of a traffic signal controller. The arrangements include a ratchet and pawl assembly cooperable to step the drum in a given direction and a motor driven gear arrangement for achieving actuation of the ratchet assembly. The gear arrangement includes a motor driven pinion in meshing engagement with an oscillatable gear segment which is connected to the ratchet assembly by a pivotal link member. A slip clutch arrangement is provided between the pinion and motor drive shaft to provide for the shaft to rotate relative to the pinion when the gear segment is stopped during movement thereof in opposite directions about its axis.

United States Patent [191 De Lille et al.

[451 Aug. 13, 1974 TRAFFIC SIGNAL CONTROLLER [75] Inventors: Richard A. De Lille, Moline;

Frederick E. Erickson, Port Byron, both of I11.

[73] Assignee: Gulf Western Industries, Inc., New

York, NY.

22 Filed: Aug. 29,1973

211 App]. No.: 392,679

3,141,344 7/1964 Nagy 74/126 Primary ExaminerSamuel Scott Assistant ExaminerF. D. Shoemaker Attorney, Agent, or Firm-Meyer, Tilberry & Body [57] ABSTRACT Structural arrangements are disclosed for achieving stepped advancement of a cam drum of a traffic signal controller. The arrangements include a ratchet and pawl assembly cooperable to step the drum in a given direction and a motor driven gear arrangement for achieving actuation of the ratchet assembly. The gear arrangement includes a motor driven pinion in meshing engagement with an oscillatable gear segment which is connected to the ratchet assembly by a pivotal link member. A slip clutch arrangement is provided between the pinionand motor drive shaft to provide for the shaft to rotate relative to the pinion when the gear segment is stopped during movement thereof in opposite directions about its axis.

18 Claims, 9 Drawing Figures PAIEME nus 1 31314 SHEEI t 0F 4 TRAFFIC SIGNAL CONTROLLER This invention relates to the art of program timers and, more particularly, to an improved traffic signa controller.

Traffic signal controllers are employed in conjunction with traffic control systems to operate traffic signals in accordance with a desired program. Such controllers generally include a rotatable cam drum having switch actuating cams spaced therealong for engaging corresponding switch devices in a desired sequence. The cam drum is stepped in a given direction to achieve switch actuation, and such stepping is generally achieved through a drive motor operatively associated with the cam drum and the energization and deenergization of which is controlled in accordance with a predetermined time program.

Heretofore, arrangements for achieving stepped advancement of the cam drum have included ratchet and pawl mechanisms actuated by an oscillatable gear segment driven by a motor through a pinion on the motor shaft which engages the teeth on the gear segment. The

motor is energized to pivot the gear segment in one di-' rection, and when the gear segment reaches a predetermined degree of rotation it is stopped, whereby the ratchet and pawl mechanism is prepared to cause advancement of the drum. The motor is then deenergized, and biasing means associated with the assembly is operable to return the gear segment to its initial position in which it is again stopped. Return movement of the gear segment provides for the ratchet and pawl mechanism to step the cam drum a desired degree in the stepping direction. When the drive motor is again energized, the preceding stepping operation is repeated.

While cam drum stepping arrangements of the foregoing character are desirable, several problems have been encountered in conjunction with the operation thereof which affect the life of various components of the assembly and particularly the drive motor. In this respect, when the gear segment engages the prepositioned stops during movement in opposite directions about its axis the gear travel is abruptly interrupted. When the gear is being driven by the motor and pinion, the pre-positioned stop is engaged prior to deenergization of the drive motor. Accordingly, rotation of the drive motor shaft and pinion is abruptly interrupted whereby considerable shock is transmitted between the teeth of the gear and pinion and through the pinion to the motor shaft. Moreover, until the motor is de-energized the rotor is locked against rotation and this, of course, causes undesirable heating of the motor components as well as the exertion of stress on the joint between the motor shaft and pinion and between the engaged teeth of the pinion and gear.

When the motor is de-energized, the biasing means returns the gear segment to its initial position and, during such return movement, the motor shaft and pinion freewheel as a result of the engagementof the pinion with the gear. When the gear reaches the predetermined stop position on return movement, the gear travel is again abruptly interrupted whereby the motor shaft and pinion are subjected to considerable shock as' a result of the momentum of the freewheeling motor shaft and pinion. Such shock imposes stress on the teeth of thegear and pinion, and on the joints between the pinion and motor shaft and between the motor shaft and rotor of the motor.

The cam drum may be stepped in the foregoing manner several hundred times in a 24 hour period, whereby the gear, pinion and motor components are subjected to such shock and stress a corresponding number of times during the same period. It will be appreciated, therefore, that these parts of the stepping assembly are subjected to considerable wear and fatigue which results in frequent shut-down of the traffic signal controller for maintenance and replacement purposes. Shutdown of the traffic signal controller is of course undesirable in that control of traffic at'the location thereof is lost during the shut-down period. Just as importantly, however, maintenance and replacement of the controller parts is expensive and time consuming.

In controllers of the foregoing character heretofore provided, the pawl mechanism is generally pivotally mounted on the gear segment which is in turn mounted coaxially with respect to the cam drum.'Accordingly, selectivity with regard to mounting of the pinion drive motor relative to the gear segment and'drum is limited. Moreover, in the absence of extreme accuracy in mounting, engagement of the teeth of the pinion with the teeth on the gear segment can produce a radial force between the axes of the drive motor shaft and gear segment which stresses these components and/or the bearings therefor and the mounting supports therefor. Still further, the structural interrelationship between the pinion, gear segment and the pawl member mounted on the gear segment defines a short shock wave path for transmission of the shock of stopping the gear segment directly to the motor and gear segment supports and to the cam drum shaft associated with the latter. The imposition of such force and shock on the components of the assembly is detrimental to continued efficiency and accuracy of operation as well as to the life of the component parts.

In accordance with the present invention, the foregoing disadvantages and others of cam drum stepping mechanisms provided heretofore are advantageously overcome. In this respect, a slip clutch mechanism is associated with the pinion and drive motor shaft which enables the shaft and pinion to slip relative to one another when movement of the gear segment is abruptly interrupted. The slip clutch arrangement preferably is provided to enable slippage to occur at each end of the gear segment travel, whereby the shock heretofore imposed on the components of the stepping mechanism is minimized as is the load on the motor when it remains energized following movement of the gear segment to one of its two positions. The reduction in shock and motor load, of course, advantageously increases the life of the components of the mechanism and reduces maintenance and replacement costs.

In accordance with another aspect of the present invention, selectivity of drive motor location relative to ing movement to the arm which carries the pawl member. This'interrela'tionship provides for increased selectivity with respect to mounting of the pinion drive motor relative to the cam drum by eliminating the necessity of mounting the motor along a prescribed path having a fixed radius relative to the cam drum. Moreover, the link interconnecting the gear segment and pivotal pawl arm effectively increases the length of the shock path between the cam drum mounting compo nents and the drive motor shaft and mounting components. Thus, any shock transmitted therebetween upon stopping of the gear segment is absorbed to a considerable extent by the arm, link and gear segment to further enhance minimization of shock imposed on the drive motor shaft and motor mounting supports and on the mounting supports for the cam drum. Accordingly, the life of these components is increased, and wear and damage to these and other components of the assembly during use is decreased together with maintenance and replacement costs.

Accordingly, it is an outstanding object of the present invention to provide an improved cam drum stepping mechanism for a traffic signal controller.

Another object is the provision of a mechanism of the foregoing character which is motor driven and in which the shock imposed on the motor and other components of the mechanism during use thereof is minimized.

Yet another object is the provision of a mechanism of the above character in which shock transmission through the components between the cam drum and drive motor is reduced.

Still another object is the provision of a mechanism of the above character which enables a more selective mounting of the drive motor relative to the cam drum than heretofore possible.

A further object is the provision of a mechanism of the foregoing character which provides for minimizing stresses and load imposed on the drive motor when the components driven by the motor reach limits of movement.

Still another object is the provision of a mechanism of the foregoing character which provides for increased life of the component parts thereof and thus a reduction in maintenance and replacement costs.

The foregoing objects, and others, will in part be obvious and in part more fully pointed out hereinafter in conjunction with the description of the accompanying drawing depicting a preferred embodiment of the stepping mechanism and in which:

FIG. 1 is a plan view of a cam drum stepping mechanism in accordance with the present invention;

FIG. 2 is an enlarged plan view, in section, of a portion of the mechanism illustrated in FIG. l;

FIG. 3 is a sectional elevation view taken along line 33 in FIG. 1;

FIG. 4 is a schematic end elevation view illustrating the positions of components of the mechanism during operation thereof;

FIG. 5 is a detailed view, in section, of a slip clutch arrangement'between the drive motor shaft and pinion;

FIG. 6 is an exploded view of the slip clutch, pinion and motor shaft components;

F IG. 7 is a view in cross section of the slip clutch arrangement illustrated in FIG. 5, the section being along line 77 in FIG. 5; v v

FIG. 8 is a detail view, in section, of a magnetic slip clutch between the drive motor shaft and pinion; and

FIG. 9 is a sectional elevation of the input component of the magnetic clutch, taken along line 9-9 in FIG. 8.

Referring now in greater detail to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only and not for the purpose of limiting the invention, a cam drum stepping mechanism for a traffic signal controller is illustrated in FIGS. 1-3 which includes a base plate 10 and a pair of generally parallel spaced apart support plates 12 and 14 extending upwardly from the base plate. Support plates 12 and 14 may be integral with base plate 10 or may be separate components suitably interconnected with the base plate such as by welding or through the use of threaded fasteners or the like. The mechanism further includes a cam drum assembly 16 comprised of a camshaft 18 carrying a plurality of cam members 20 which are suitably mounted on the shaft for rotation therewith. In a manner well known, cam members 20 are operatively associated with corresponding make-break contacts 22 so that the latter are actuated in response to rotation of the cam drum. Cam drum 16 extends between support plates 12 and 14 and has the corresponding ends of shaft 18 suitably supported thereby for rotation of the cam drum relative thereto.

Cam drum 16 is adapted to be rotated step-by-step in a given direction by means of a motor driven ratchet v and pawl assembly operatively associated with the cam drum at one of the ends thereof. More particularly, in the embodiment illustrated, the motor driven ratchet and pawl assembly includes an electric drive motor 24 mounted on a support plate 26 by means of bolts or the like 28 extending through plate 26 and into the motor housing. While not illustrated in detail, it will be appreciated that support plate 26 for the motor can be suitably interconnected with-base plate 10 and/or support plate 12 to support the motor in a desired position relative to the cam drum. Motor 24 includes a drive shaft 30, and the motor is adapted to rotate pinion gear 32 through a slip clutch mechanism 34 which is described in greater detail hereinafter. The teeth of pinion 32 are in meshing engagement with the teeth of gear segment 36 which is mounted on support plate 12 for rotation relative thereto. More particularly, gear 36 is mounted on a gear shaft 38 which is provided with a sleeve bearing 40. One end of shaft 38 is provided with a suitable retaining ring 42 for gear 36, and the other end of the shaft extends through an opening in support plate 12 and is provided with a threaded shank adapted to receive threaded nut 44, whereby the shaft and gear are removably mounted on support plate 12.

The motor driven ratchet and pawl assembly further includes an oscillatable pawl arm 46 having a pivot axis coaxial with the axis of cam drum shaft 18. In this respect, support plate 12 carries a stub shaft 48 which projects inwardly from support plate 12 and has its inner end disposed in an axial opening 50 in camshaft 18. The camshaft is supported for rotation relative to stub shaft 48 by means of a sleeve bearing 52 interposed between shaft 48 and recess 50. Pawl arm 46 is provided with an opening 54, and a bearing sleeve 56 is disposed in opening 54 and surrounds shaft 48,

whereby pawl arm 46 is supported for pivotal movement relative to shaft 48 and independent of the rotatable support of camshaft 18. A positioning sleeve 58 surrounds bearing sleeve 56 and is interposed between pawl arm 46 and sleeve 60 which is suitably secured to shaft 48 and is disposed in bearing block 62 mounted in an opening therefor in support plate 12. A biasing spring 64 surrounds sleeve 58 and has an end 65 engaged behind a pawl member 66 on arm 46 so that the arm is biased in a given direction, as explained more fully hereinafter. It will be appreciated that the other end of spring 64, not illustrated, is secured against movement when arm 46 pivots opposite the given direction so that the spring stores energy to bias the arm in the given direction.

Pawl member66 is mounted-on pawl arm 46 for movement therewith and pivotal movement relative thereto. In this respect, pawl arm 46 is provided with an opening in which a support sleeve 68 is fixedly mounted to receive and support a removable pawl member shaft 70. Shaft 70 has a head 72 at one end and a threaded shank at its opposite end adapted to receive a nut 74 by which the shaft is removably secured within sleeve 68. Pawl member 66 surrounds shaft 70 at the headed end thereof and is pivotal relative to the shaft. A biasing spring 76 surrounds the pawl member and is operatively associated therewith and with arm 46 in a well known manner to bias the pawl member to pivot in a desired direction relative to the arm, as described hereinafter.

A ratchet member 78 is suitably mounted on camshaft 18 for rotation therewith. Ratchet member 78 has teeth 80, and paw] member 66 has a nose portion 82 cooperable with ratchet teeth 80 to advance the cam drum 'in response to operation of the motor driven ratchet and pawl mechanism. A pivotal, spring biased holding finger 84 is mounted on base plate to engage ratchet teeth 80 to prevent rotation of the cam drum in the direction opposite to the stepping direction. A spring 86 biases holding finger 84 into engagement with ratchet teeth. The holding finger is suitably mounted on a bracket assembly 88 which is provided with a stop member 90 to engage and limit pivotal movement of pawl arm 46 in the direction of stepping movement of the cam drum. Support plate 12 is provided with a stop member 92 which is mounted thereon in a position to engage gear segment 36 to limit movement of the latter in the direction which results in movement of pawl arm 46 in the direction opposite the stepping direction. A link element 94 pivotally interconnects pawl arm 46 and gear segment 36. Any suitable connection can be employed and, in the embodiment illustrated, link 94 has its opposite ends apertured to receive a pin 93 integral with gear 36 adjacent the outer periphery thereof and a pin 95 integral with the outer end of arm 46. Suitable fasteners, such as split rings 97, can be attached to pins 93 and 95 to retain the link thereon.

Prior to a stepping operation the component parts of the mechanism are in the positions thereof illustrated in FIG. 3, which positions correspond to the broken line positions of the components illustrated schematically in FIG. 4. When motor 24 is energized to achieve a stepping operation, pinion 32 is rotated to pivot gear segment 36 counterclockwise from the position illustrated in FIG. 3 to the solid position illustrated in FIG. 4. This degree of rotation of gear 36 corresponds to the necessary movement of pawl 66 relative to ratchet 78 to position pawl nose 82 relative to ratchet teeth 80 to achieve a desired degree or rotation of the cam drum during the stepping operation. When the component parts reach the position illustrated by solid lines in FIG. 4, gear 36 engages stop 92 whereby further pivotal movement of gear 36 and thus pawl arm 46 is precluded. During movement of gear 36 towards engagement with stop 92, spring 64 associated with pawl arm 46 is wound up to store a return biasing force for arm 46, and pawl 66 is displaced relative to teeth of ratchet wheel 78 so that it will engage a tooth of the ratchet wheel and advance the cam drum in response to return movement of pawl arm 46. Pawl spring 76 biases nose 82 toward the ratchet wheel to assure engagement of the nosewith the ratchet teeth.

When the component parts reach the position illustrated by solid lines in FIG. 4, motor 24 is still energized. Upon de-energization of the motor, spring 64 biases pawl arm 46 counter-clockwise with respect to FIGS. 3 and 4, whereby the pawl arm and gear segment 36 are returned to their initial position and pawl nose 82 engages behind a ratchet tooth to advance the cam drum. During return movement of the components, pinion 32 and motor shaft 30 freewheel as a result of de-energization of motor 24. When the component parts reach their initial positions, pawl member 66 engages fixed stop to preclude further movement of the components in the return direction. Engagement of pawl member 66 with stop 90 prepares the components of the assembly for a subsequent stepping operation when motor 24 is again energized. Energization and deenergization of motor 24 is achieved in accordance with a time program and associated circuitry of the traffic controller, not illustrated.

When gear segment 36 engages fixed stop 92, and

when ratchet member 66 engages fixed stop 90, it will be appreciated that considerable stress is imposed on the pinion and gear segment as well as on the motor shaft and other components of the assembly as a result of the abrupt interruption of the movement-of the components. In accordance with the present invention, the detrimental effect of such stress is advantageously reduced by the gear segment, link and pawl arm arrangement which together define an elongated path for the transmission of such stress between the components, whereby a considerable portion of the stress is absorbed in the components themselves. Further in accordance with the present invention, the imposition of stress on the motor shaft and between the teeth of the pinion and gear segment is advantageously reduced by the provision of slip clutch assembly 34 between the motor shaft and pinion. Many suitable slip clutch arrangements can be devised to achieve the desired result, and one such arrangement is illustrated in FIGS. 5-7 of the drawing.

In the disclosed arrangement, motor shaft 30 is provided on its outer end with a sleeve which is secured to shaft 30 for rotation therewith such as by a pin 102 extending through the sleeve and a corresponding opening in the shaft. Sleeve 100 has an inner portion 104 and an outer portion 106, whereby the sleeve is longitudinally stepped to define an inner shoulder 108 and an outer shoulder 110. Pinion 32 is mounted on sleeve 100 for rotation relative thereto and is provided with a hub portion 112 overlying outer portion 106 of the sleeve. Hub portion 112 has an outer diameter generally corresponding to the outer diameter of inner portion 104 of sleeve 100. Pinion 32 is retained axially on sleeve 100 by means of a suitable retainer ring or the like 114 removably interconnected with shaft 30. A coiled clutch spring 116 is wrapped around and frictionally engages inner portion 104 of sleeve 100, and

a second coiled clutch spring 118 is wrapped around and frictionally engages hub portion 112 of pinion 32. A washer 17 is disposed between the springs. A clutch actuating member in the form of an annular sleeve 120 loosely surrounds springs 116 and 118 and is loosely retained axially between sleeve 100 and pinion 32 by shoulder 108 of sleeve 100 and the opposed inner face of pinion 32. Sleeve 120 is provided on one side thereof with a longitudinally extending slot 122 extending from one end of the sleeve to about the longitudinal center point thereof. A second longitudinal slot 124 is provided in sleeve 120 on the side thereof opposite the side provided with slot 122. Slot 124 extends longitudinally v of sleeve 120 from the opposite end of the sleeve to a point generally midway of the length thereof. Coil spring 116 is provided with a radially projecting end finger 126 which extends loosely into slot 122, and coil spring 118 is provided with a radially projecting end finger 128 which extends loosely into slot 124.

In the direction of view illustrated in FIG. 7, coil spring 116 is wrapped counterclockwise about inner portion 104 of sleeve 100 and from finger 126 thereof towards shoulder 108. The end of spring 116 adjacent shoulder 108 is free of any fixed interconnection with sleeve 100, whereby the spring merely frictionally engages inner portion 104 of sleeve 100. Coil spring 118, as viewed in FIG. 7, is wrapped clockwise about hub 112 of the pinion from the inner face of gear 32 to end finger 128. The end of spring 118 adjacent pinion 32 is free of fixed interconnection with hub 122, whereby the spring only frictionally engages hub portion 112.

Since springs 116 and 118 frictionally engage the underlying portion of sleeve 100 and hub 112, respectively, it will be appreciated that the springs tend to rotate with the corresponding underlying portion of the sleeve and hub. The clockwise and counterclockwise configuration of the springs, together with slotted actuator sleeve 120, provide for sleeve 100 and thus shaft 30 to slip relative to pinion 32 when the pinion is held in a given position and shaft 30 is rotated in either direction relative to its axis. In this respect, if pinion 32 is held against rotation and shaft 30 is rotated clockwise as viewed in FIG. 7, spring 116 will rotate with sleeve 100 so that the right hand side of finger 126 engages the right hand side of slot 122 of actuating sleeve 120. This engagement moves sleeve 120 clockwise so that the right hand side of slot 124 engages the right hand side of finger 128 of spring 118. The engagement of finger 126 with slot 122 tends to unwind spring 116 while the engagement of slot 124 with finger 128 tends to tighten spring 118 relative to hub 112. Accordingly, finger 128 locks sleeve 120 against rotation relative to sleeve 7 100 and motor shaft 30 and the frictional contact between spring 116 and underlying portion 104 of sleeve 100 is decreased whereby sleeve 100 and thus shaft 30 slip relative to pinion 32. I

When motor shaft'30 is rotating counterclockwise as viewed in FIG. 7 and pinion 32 is held against rotation,

the left hand side of finger 126 of spring 116 engages the left hand side of slot 122 in the actuating sleeve tending to tighten spring 116 about portion 104 of sleeve 100. Engagement of finger 126 with slot 122 in this manner rotates sleeve 120 counterclockwise 8 whereby the left hand side of sleeve slot 124 engages the left hand side of finger 128 of spring 118, whereby sleeve 120 tends to unwind spring 118 relative to hub 112 of pinion 32. This reduction of the frictional engagement between spring 1 l8 and hub 112 provides for sleeve 100 and thus shaft to slip relative to pinion 32. It will be appreciated, therefore, that sleeve 100 and thus motor shaft 30 is adapted to slip relative to pinion 32 upon stoppage of pinion 32 when shaft 30 is rotating in either direction relative to its axis.

The foregoing slip clutch arrangement advantageously provides for slippage between pinion 32 and .the drive motor shaft when gear segment 36 is moved .to either of its limits of movement during a cam drum stepping operation. More particularly, when motor 24 is energized to rotate pinion 32 clockwise as viewed in FIGS. 3 and 4 to pivot gear segment 36 counterclockwise so that pawl arm 46 displaces pawl member 66 relative to ratchet gear 78, gear segment 36 engages fixed stop 92 prior to de-energization of the drive motor. Accordingly, the slip clutch arrangement allows the motor shaft to continue to rotate subsequent to engagement of gear segment 36 with stop 92. This advantageously reduces the shock on the motor shaft and between the teeth of the pinion and gear segment in response to the abrupt stopping of the gear segment, and allows the I motor to continue to operate under a reduced load from thatimposed thereon in the absence of a slip clutch arrangement. When the drive motor is deenergized, biasing spring 64 associated with ratchet arm 36 returns the ratchet arm and thus gear segment 36 to their initial dispositions and during this return movement pinion 32 and drive motor shaft 30 freewheel as a result of de-energization of the motor. When the components return to their initial position they are abruptly stopped by engagement of pawl member 66 with fixed stop 90. Motor shaft 30 has considerable momentum as a result of the return movement, and the slip clutch arrangement provides for the drive shaft to rotate relative to pinion 32 when the latter stops, thus to reduce the shock imposed on the teeth of the pinion and gear segment and which would otherwise be transmitted from the pinion to the motor shaft.

Preferably, the frictional grip of springs 116 and 118 relative to the underlying portions of sleeve and hub 112, respectively, are different from one another, whereby the respective slippages of pinion 32 relative to sleeve 100 and drive shaft 30 occur upon the imposition of different torsional loads therebetween. More particularly, it will be appreciated that slippage between the pinion and motor shaft when the motor is energized and the gear segment engages fixed stop 92 must be such as to provide for the gear segment to be retained against fixed stop 92 and against the return bias of spring 64 until such time as motor 24 is deenergized. Thus, in the arrangement illustrated, the frictional engagement between spring 118 and hub 112 of pinion 32 must be sufficient to prevent premature return movement of gear segment 36. Spring 116 provides the slippage between the pinion and motor shaft when gear segment 36 stops in its initial position and, while the frictional engagement of spring 116 with sleeve portion 104 could be the'same as that between spring 118 and hub 112, it is preferred to provide for the frictional engagement of spring 116 with sleeve portion 104 to be less so that slippage occurs at a lesser torsional load between spring 116 and sleeve portion 104. This relationship enables minimizing the shock imposed on the teeth on the pinion and gear segment and on the drive motor shaft when the components are stopped in their initial positions.

A further slip clutch arrangement is illustrated in FIGS. 8 and 9 of the drawing. In this embodiment a magnetic clutch assembly is illustrated comprised of an input clutch component 130 mounted on motor shaft 30 for rotation therewith, and an output clutch component 132 supported by shaft 30 for rotation relative thereto and relative to clutch component 130. As set forth more fully hereinafter, pinion 32 is interconnected with output component 132 for rotation therewith relative to motor shaft 30. Clutch components 130 and 132 are magnetically attracted to one another, whereby pinion 32 is adapted to rotate with motor shaft 30 until the torsional load between pinion 32 and shaft 30 overcomes the magnetic force between the two clutch components. When the magnetic force is overcome, clutch components 130 and 132 rotate relative to one another, whereby motor shaft 30 can rotate relative to pinion 32.

In the embodiment disclosed, input clutch component 130 is comprised of inner and outer rings 134 and 136, respectively, of magnetic material such as steel. Rings 134 and 136 are concentric with respect to the axis of shaft 30 and are radially spaced apart to receive a permanent magnet ring 138 therebetween. Prefera bly, magnet ring 138 is a flexible permanently magnetized rubber material having radially opposite faces of different polarity. A suitable permanently magnetic material of this character is produced by Minnesota Minning and Manufacturing Company and is available under the trademark PLASTIFORM which is a registered trademark of the latter company. In the embodiment disclosed, magnet ring 138 is oriented relative to rings 134 and 136 so as to induce a South polarity in inner ring 134 and a North polarity in outer ring 136. The radial space between inner and outer rings 134 and 136 can be such as to snugly receive ring 138, and the three rings are provided with apertures to receive fasteners such as set screws 140 which are of nonmagnetic material and by which the input clutch component is fastened to motor shaft 30 for rotation therewith. Fasteners 140, in addition to interconnecting the clutch component with motor shaft 30, serve to main tain rings 134, 136 and 138 in assembled relationship relative to one another. It will be appreciated, however, that the three rings may be otherwise interconnected against displacement relative to one another and that the input clutch component can be interconnected with the motor shaft other than by fasteners such as set screws.

Output clutch component 132 is, to a certain extent, structurally similar to input component 130. In this respect, output component 132 is comprised of inner and outer rings 142 and 144, respectively, of magnetic material such as steel. Rings 142 and 144 are concentric with respect to the axis of motor shaft 30 and are radially spaced apart to receive a permanent magnet ring 146 similar to permanent magnet ring 138. In this instance, however, permanent magnet ring 146 is oriented relativeto inner and outer rings 142 and 144 such as to induce a North polarity in inner ring 142 and a South polarity in outer ring 144. As mentioned hereinabove, the permanent magnet material has opposite faces of different polarity, whereby the desired polarity for rings 142 and 144 is achieved by reversing the surface relationship of magnet ring 136 relative to the inner and outer rings.

In a manner similar to input component 130, rings 142, 144 and 146 of output component 132 are apertured to receive fasteners 148 of non-magnetic material for retaining the rings in assembled relationship and for interconnecting the output component with pinion 32. In this respect, it will be noted that the aperture through inner ring 142 for receiving motor shaft 30 is enlarged from the outer end thereof towards the inner end to receive a sleeve 150 of pinion 32. Fasteners 148 engage sleeve 150 to interconnect output component 132 with pinion 32 for rotation therewith. Pinion 32 and sleeve 150 thereof are, of course, apertured to loosely receive drive shaft 30 so as to be rotatable relative thereto. Preferably, the outer end of shaft 30 is slotted to receive a split retaining ring 152 to prevent unintentional axial displacement of output component 132 and pinion 32 from the drive shaft.

It will be seen that the magnetic orientation between the axially opposed inner and outer concentric rings of the two clutch components provides for the components to be magnetically attracted to one another. Preferably, the inner rings of the two components are of like radial dimension in the direction transverse to the axis of shaft 30 and, similarly, the outer rings of the two components are of like dimension in the same direction. Further, the inner end faces 134a and 136a of rings 134 and 136 preferably are coplanar, and the inner end faces 142a and 144a of rings 142 and 144 are coplanar. This relationship provides for the end faces of the two clutch components to have a maximum area of surface engagement therebetween. It will be appreciated,.however, that the coplanar end face relationship as well as the transverse dimensional identity can be varied without departing from the relationship required to achieve magnetic attraction between the two components.

It will be apparent from the foregoing description that rotation of motor shaft 30 and input clutch component therewith is adapted to impart rotation to pinion 32 through output component 132, and that shaft 30 is adapted to rotate relative to pinion 32 when the latter is stopped or otherwise loaded to the extent that the torsional load between the pinion and drive shaft overcomes the force of magnetic attraction between components 130 and 132. The torsional load at which such slippage occurs can be varied in several different ways. For example, the areas of contact between the end faces of the ring components can be increased or decreased by changing the radial dimensions of the ring elements. Alternatively, the surfaces of the end faces can be machined to different degrees of finish to increase or decrease frictional engagement therebetween. Many modifications of the structure disclosed will be readily apparent to provide for achieving slippage at a desired torsional load between the components.

While considerable emphasis has been placed herein on a particular gear segment, link and pawl arm configuration, it will be appreciated that other arrangements of these components can readily be employed to achieve the desired result and that the particular arrangement devised will vary with the desired location for mounting the drive motor relative to the remainder of the mechanism. Further, it will be appreciated that 1 1 other arrangements of slip clutch mechanisms between the pinion and motor drive shaft can readily be devised to achieve the desired end result and that the particular arrangements herein disclosed can be modified without departing from the principals of operation thereof. Moreover, it will be understood that while it is desirable to provide a slip clutch arrangement operable to provide slippage between the pinion and drive shaft in response to drive shaft rotation in opposite directions relative to the pinion, the advantages provided by a slip clutch can be achieved to a lesser extent but still satisfactorily by providing for such slippage in only one direction and in response to movement of the components to either one or the other of the endmost positions thereof during use of the stepping mechanism. Further, it will be understood that the advantages derived by use of a slip clutch arrangement are independent of the necessity of a gear segment, link and pawl arm assembly and, therefore, can be employed to provide the same advantage in stepping mechanisms other than that specifically illustrated and described herein. Since many possible embodiments of the present invention may be made and since many possible changes may be made in the embodiments herein illustrated and described, it is to be distinctlyunderstood that the foregoing descriptive matter is to be interpreted merely as illustrative of the present invention and not as a limitation.

Having thus described our invention, we claim:

1. In a traffic signal controller, a base, spaced apart support means on said base, a cam drum mounted between said support means for stepped movement, a ratchet wheel fixed to said drum, arm means including an arm oscillatable relative to said ratchet wheel and a pawl pivotally mounted on said arm and cooperable with said ratchet wheel to step said drum in a given direction, means to prevent reverse movement of said drum, resilient means biasing said arm in said given direction, and means to displace said arm against the bias of said resilient means to cooperably position said pawl relative to said ratchet wheel, said displacing means including oscillatable gear means, a pinion for displacing said gear means, drive means including a motor for rotating said pinion to displace said gear means, and link means interconnecting said gear means and arm.

2. In a controller according to claim 1, stop means positioned for engagement by said gear means to limit movement of said gear means in the direction to displace said arm against the bias of said resilient means.

3. In a controller according to claim 2, stop means positioned for engagement by said arm means to limit movement of said arm in said given direction.

4. In a controller according to claim 2, said motor including drive shaft means, and slip clutch means between said drive shaft means and pinion operable in response to engagement of said gear means with said stop means therefor.

5. In a controller according to claim 3, said motor including drive shaft means, and slip clutch means between said drive shaft means and pinion operable in response to engagement of said arm means with said stop means therefor.

6. In a controller according to claim 3, said motor including drive shaft means, and slip clutch means between said drive shaft means and pinion operable to permit slippage between said shaft means and pinion 12 when said gear means and said arm means engage the respective stop means-therefor.

7. In a controller according to claim 1, said gear means being mounted on one of said spaced apart support means for oscillation about a fixed axis, said pinion being rotatable about a second axis, and said link means being pivotally connected to said gear means at a third axis, said first axis being between said second and third axes.

8. In a controller according to claim 3, said second mentioned stop means being positioned to be engaged by said pawl on said arm.

9. In a traffic signal controller, a cam drum, means supporting said cam drum for stepped movement, a ratchet wheel fixed to said drum, and means for indexing said drum, said indexing means including gear means pivotal between first and second positions, pawl means, means interconnecting said gear means and pawl means for said 'pawl means to cooperate with said ratchet yvhe el to step said drum inresponse to movement of said gear means betweensafi first and second positions, a pinion for'displacing said gear means, a motor for rotating said pinion to pivot said gear means from said first position to said second position, means biasing said gear means to pivot from said second position to said first position, means to stop said gear means in said first and second. positions, said motor having drive shaft means, and slip clutch means between said drive shaft means and pinion operable when said gear means is stopped in at least one of said first and second positions to permit said drive shaft means to rotate relative to said pinion.

10. In a controller according to claim 9, said slip clutch means being operable when said gear means is stopped in said first and said second positions. 11. In a controller according to claim 10, said slip clutch means being operable to permit said drive shaft means to rotate relative to said pinion at given torsional loads therebetween when said gear means is stopped in said first and second positions, said given torsional load in said second position being greater than said given torsional load in said first position.

12. In a controller according to claim 11, said means biasing said gear means to pivot from said second position to said first position including resilient means for storing energy when said motor rotates said pinion to pivot said gear means from said first position to said second position.

13. In a controller according to claim 11, said pawl means including an arm oscillatable relative to said ratchet wheel and a pawl pivotally mounted on said arm, and said means interconnecting said gear means and pawl means including link means pivotally connected to said arm and to said gear means.

14. In a controller according to claim 10, said clutch means including a pair of coil springs, a first of said coil springs frictionally engaged around said drive shaft means, said pinion including a hub rotatably supported by said drive shaft means, the second of said coil springs frictionally engaged around said hub, said coil springs being wound in opposite directions with respect to the axis of said drive shaft means, and actuating means for said coil springs operable in response to rotation of said drive shaft means in opposite directions to, respectively, wind and unwind said first coil spring relative to said drive shaft means and to unwind and wind said second coil spring relative to said hub.

15. In a controller according to claim 14, one of first and second coil springs being in tighter frictional engagement with the corresponding one of said drive shaft means and hub than the other of said coil springs.

springs, and said sleeve means including means engaging said actuating ends of said coil springs to bias said actuating ends in opposite directions in response to rotation of said drive shaft means in opposite directions.

18. In a controller according to claim 17, said actuating ends of said coil springs extending radially outwardly with respect to the axis of said drive shaft means, and said sleeve means including openings receiving said ends. 

1. In a traffic signal controller, a base, spaced apart support means on said base, a cam drum mounted between said support means for stepped movement, a ratchet wheel fixed to said drum, arm means including an arm oscillatable relative to said ratchet wheel and a pawl pivotally mounted on said arm and cooperable with said ratchet wheel to step said drum in a given direction, means to prevent reverse movement of said drum, resilient means biasing said arm in said given direction, and means to displace said arm against the bias of said resilient means to cooperably position said pawl relative to said ratchet wheel, said displacing means including oscillatable gear means, a pinion for displacing said gear means, drive means including a motor for rotating said pinion to displace said gear means, and link means interconnecting said gear means and arm.
 2. In a controller according to claim 1, stop means positioned for engagement by said gear means to limit movement of said gear means in the direction to displace said arm against the bias of said resilient means.
 3. In a controller according to claim 2, stop means positioned for engagement by said arm means to limit movement of said arm in said given direction.
 4. In a controller according to claim 2, said motor including drive shaft means, and slip clutch means between said drive shaft means and pinion operable in response to engagement of said gear means with said stop means therefor.
 5. In a controller according to claim 3, said motor including drive shaft means, and slip clutch means between said drive shaft means and pinion operable in response to engagement of said arm means with said stop means therefor.
 6. In a controller according to claim 3, said motor including drive shaft means, and slip clutch means between said drive shaft means and pinion operable to permit slippage between said shaft means and pinion when said gear means and said arm means engage the respective stop means therefor.
 7. In a controller according to claim 1, said gear means being mounted on one of said spaced apart support means for oscillation about a fixed axis, said pinion being rotatable about a second axis, and said link means being pivotally connected to said gear means at a third axis, said first axis being between said second and third axes.
 8. In a controller according to claim 3, said second mentioned stop means being positioned to be engaged by said pawl on said arm.
 9. In a traffic signal controller, a cam drum, means supporting said cam drum for stepped movement, a ratchet wheel fixed to said drum, and means for indexing said drum, said indexing means including gear means pivotal between first and second positioNs, pawl means, means interconnecting said gear means and pawl means for said pawl means to cooperate with said ratchet wheel to step said drum in response to movement of said gear means between said first and second positions, a pinion for displacing said gear means, a motor for rotating said pinion to pivot said gear means from said first position to said second position, means biasing said gear means to pivot from said second position to said first position, means to stop said gear means in said first and second positions, said motor having drive shaft means, and slip clutch means between said drive shaft means and pinion operable when said gear means is stopped in at least one of said first and second positions to permit said drive shaft means to rotate relative to said pinion.
 10. In a controller according to claim 9, said slip clutch means being operable when said gear means is stopped in said first and said second positions.
 11. In a controller according to claim 10, said slip clutch means being operable to permit said drive shaft means to rotate relative to said pinion at given torsional loads therebetween when said gear means is stopped in said first and second positions, said given torsional load in said second position being greater than said given torsional load in said first position.
 12. In a controller according to claim 11, said means biasing said gear means to pivot from said second position to said first position including resilient means for storing energy when said motor rotates said pinion to pivot said gear means from said first position to said second position.
 13. In a controller according to claim 11, said pawl means including an arm oscillatable relative to said ratchet wheel and a pawl pivotally mounted on said arm, and said means interconnecting said gear means and pawl means including link means pivotally connected to said arm and to said gear means.
 14. In a controller according to claim 10, said clutch means including a pair of coil springs, a first of said coil springs frictionally engaged around said drive shaft means, said pinion including a hub rotatably supported by said drive shaft means, the second of said coil springs frictionally engaged around said hub, said coil springs being wound in opposite directions with respect to the axis of said drive shaft means, and actuating means for said coil springs operable in response to rotation of said drive shaft means in opposite directions to, respectively, wind and unwind said first coil spring relative to said drive shaft means and to unwind and wind said second coil spring relative to said hub.
 15. In a controller according to claim 14, one of first and second coil springs being in tighter frictional engagement with the corresponding one of said drive shaft means and hub than the other of said coil springs.
 16. In a controller according to claim 15, said second coil spring being in tighter frictional engagement with said hub than the frictional engagement of said first coil spring with said drive shaft means.
 17. In a controller according to claim 16, each said coil springs having an actuating end, said actuating means including sleeve means surrounding said coil springs, and said sleeve means including means engaging said actuating ends of said coil springs to bias said actuating ends in opposite directions in response to rotation of said drive shaft means in opposite directions.
 18. In a controller according to claim 17, said actuating ends of said coil springs extending radially outwardly with respect to the axis of said drive shaft means, and said sleeve means including openings receiving said ends. 